     :first :head}))
 
 ;; h21a is a specialization of h21. it's used for vp-aux to prevent over-generation.
-(def h21a
+(defonce h21a
   (merge
    (unify
     h21

    :schema-symbol 'h32 ;; used by over-each-parent to know where to put children.
    :first :head}))

(def c00
  (unify-check
   head-last
   {:comment "c00"

      :comp {:italiano comp-italian}
      :italiano {:a head-italian
                 :b comp-italian}})))
(defonce head-last
  (let [head-italian (atom :top)
        comp-italian (atom :top)
        head-cat (atom :top)
